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yacc

NAME

Yacc - an LALR(1) parser generator

SYNOPSIS

yacc [ -dglrtv ] [ -b file_prefix ] [ -p symbol_prefix ] filename

DESCRIPTION

Yacc reads the grammar specification in the file filename and generates an LALR(1) parser for it. The parsers consist of a set of LALR(1) parsing tables and a driver routine written in the C programming language. Yacc normally writes the parse tables and the driver routine to the file y.tab.c.

The following options are available:

-b file_prefix

The -b option changes the prefix prepended to the output file names to the string denoted by file_prefix. The default prefix is the character y.

-d

The -d option causes the header file y.tab.h to be written.

-g

The -g option causes a graphical description of the generated LALR(1) parser to be written to the file y.dot in graphviz format, ready to be processed by dot(1).

-l

If the -l option is not specified, yacc will insert #line directives in the generated code. The #line directives let the C compiler relate errors in the generated code to the user's original code. If the -l option is specified, yacc will not insert the #line directives. #line directives specified by the user will be retained.

-o output_file

specify the filename for the parser file. If this option is not given, the output filename is the file prefix concatenated with the file suffix, e.g., y.tab.c. This overrides the -p option.

-p symbol_prefix

The -p option changes the prefix prepended to yacc-generated symbols to the string denoted by symbol_prefix. The default prefix is the string yy.

-P

create a reentrant parser, e.g., "%pure-parser".

-r

The -r option causes yacc to produce separate files for code and tables. The code file is named y.code.c, and the tables file is named y.tab.c.

-t

The -t option changes the preprocessor directives generated by yacc so that debugging statements will be incorporated in the compiled code.

-v

The -v option causes a human-readable description of the generated parser to be written to the file y.output.

-V

print the version number to the standard output.

EXTENSIONS

yacc provides some extensions for compatibility with bison and other implementations of yacc:

%expect number

tell yacc the expected number of shift/reduce conflicts. That makes it only report the number if it differs.

%expect-rr number

tell yacc the expected number of reduce/reduce conflicts. That makes it only report the number if it differs. This is (unlike bison) allowable in LALR parsers.

%pure-parser

Most variables (other than yydebug and yynerrs) are allocated on the stack within yyparse, making the parser reasonably reentrant.

DIAGNOSTICS

If there are rules that are never reduced, the number of such rules is reported on standard error. If there are any LALR(1) conflicts, the number of conflicts is reported on standard error.